The number one cause of Software bugs is the Specification. There are several reasons specifications are the largest bug producer.
In many instances a Spec simply isn’t written. Other reasons may be that the spec isn’t thorough enough, its constantly changing, or it’s not communicated well to the entire team. Planning software is vitally important. If it’s not done correctly bugs will be created.
The next largest source of bugs is the Design, That’s where the programmers lay the plan for their Software. Compare it to an architect creating the blue print for the building, Bugs occur here for the same reason they occur in the specification. It’s rushed, changed, or not well communicated.
Coding errors may be more familiar to you if you are a programmer. Typically these can be traced to the Software complexity, poor documentation, schedule pressure or just plain dump mistakes. It’s important to note that many bugs that appear on the surface to be programming errors can really be traced to specification. It’s quite common to hear a programmer say, “ oh, so that’s what its supposed to do. If someone had told me that I wouldn’t have written the code that way.”
The other category is the catch-all for what is left. Some bugs can blamed for false positives, conditions that were thought to be bugs but really weren’t. There may be duplicate bugs, multiple ones that resulted from the square root cause. Some bugs can be traced to Testing errors.
Costs: The costs re logarithmic- that is, they increase tenfold as time increases. A bug found and fixed during the early stages when the specification is being written might cost next to nothing, or 10 cents in our example. The same bug, if not found until the software is coded and tested, might cost $1 to $10. If a customer finds it, the cost would easily top $100.
